Tensor-polarized gluon distribution \texorpdfstring{$h_{1TT}^g$}{h1TTg} in the deuteron: QCD evolution and Drell-Yan phenomenology

Abstract

We study the QCD evolution of the tensor-polarized double-helicity-flip gluon distribution $h_{1TT}^g$ in the deuteron and its impact on proton-deuteron Drell-Yan production. The nonperturbative input is taken from the spin-1 spectator model and evolved at leading order with the autonomous gluon evolution equation. The uncertainty of the model fit is propagated to the tensor-polarized cross-section difference and the asymmetry $A_{E_{xy}}$ using an ensemble of 100 replicas. Compared with the earlier benchmark estimate based on a longitudinally polarized gluon distribution, the evolved spectator-model input gives smaller cross sections in most of the kinematic region and a much stronger decrease of $|A_{E_{xy}}|$ with $Q^2$. At sufficiently large center-of-mass energy, the asymmetry varies only slowly with $\sqrt{s}$, whereas the low-$\sqrt{s}$ and large-$Q^2$ regions probe the poorly constrained large-$x$ tail of the model. We also evolve the tensor-polarized gluon distribution $f_{1LL}^g$ in the coupled singlet-gluon system and assess its contribution to the reference cross-section sum. Its effect remains moderate in the kinematic region where the spectator-model prediction is under reasonable control.

arXiv comment11 pages, 9 figures